Gardai are treating the deaths - one of the worst to hit the Inishowen area of Donegal - as a tragic accident.

The family are from Derry, with one of Ms Daniels’ sons, Joshua, playing for Derry City FC.

The Audi car driven by Mr McGrotty is believed to have been turning at the end of the pier in Buncrana when the wheels failed to grip.

The slipway structure, used by vehicles to access a ferry back and forth across Lough Swilly to Rathmullan in the summer, is prone to a build-up of thick algae.

Ms McGrotty was able to see her baby girl last night in Letterkenny General Hospital and she is said to be “doing well”.

Emergency rescue crews, including local RNLI lifeboats based on the Swilly, were on the scene within minutes of the alarm being raised by a passer-by.

Eyewitness Francis Crawford said he watched Mr McGrotty scream for help as the Audi slid in to the sea off the pier.

“The man was still shouting to me when the car went down. It was very sad,” he said. “There was nothing I could do, or nothing anybody could do.

“Any of the people who could do something were coming as quick as they could and got here in great time and knew what to do.

“But it was all too late. There was nothing anybody could do. Everybody did what they could and it was too late.”

Mr Crawford said he asked another passer-by to swim out to the car as it edged, nose first, into deeper water.

The man from Kerrykeel, Co Donegal, stripped down to his underwear to take the baby from the car just as it drifted off the slipway and began to sink in about 12 feet of freezing water.

“How he got (the baby) ... they are saying it was handed out to him,” Mr Crawford said.

“When he came back he was totally exhausted. I think if he had another five yards to go - I can’t see how he would have made it.”

Mr Crawford said he was a hero who had risked his life.

The pier is a very popular scenic spot, with hundreds of day-trippers visiting the area from Derry city and the north west every weekend.

Mr Crawford described the panic that ensued with the car sinking within minutes of it sliding down the slipway.

“All the time the car was bobbing about and I knew the services were all on their way and I was hoping against hope that the car would stay up until the people came,” he said.

“I was watching the car and the nose of it started to dip and then all of a sudden the whole of it started to go down, nose first, and everything stopped.”

A major air and sea rescue mission was mounted by the Irish Coast Guard, gardai and emergency services after the alarm was raised.

Two lifeboats, a helicopter and local fishing boats were involved in the efforts.

Mr Crawford broke down in tears recalling the final moments, and three of the occupants drowning after freeing themselves from the car.

“It was harrowing and heart-rending,” he said.

“I don’t want to go into details.

“Feeling hopeless and helpless. Nothing you could do and the man (driver) was shouting to me and I said ‘I’ve phoned them, everyone is on their way’ and he was still shouting.

“You felt so hopeless and you watched it unfolding in front of your eyes.

“It was a surreal sort of thing.”

A book of condolences is to open in Derry in coming days.

Mayor of Derry City and Strabane District Council Elisha McCallion said: “This is a terrible tragedy that has affected the entire community in Derry and Donegal and left all of us numb.

“Who would have thought that a family day out could have ended so tragically? It is beyond belief and I can’t put into words how sorry I am for the family and those affected by this dreadful accident.”

Bishop of Derry Donal McKeown is to spend time with the family this afternoon.

First Minister Arlene Foster issued a joint statement with Mr McGuinness to express sorrow over the deaths.

“We share the widespread sorrow following the tragedy that claimed the lives of five people, including two children, in County Donegal yesterday,” they said.

“This tragedy resonates with us all. At times like this it is difficult to comprehend how life can be so altered in the matter of moments.

“Our thoughts and prayers are with the family and friends of those killed, those who tried to help and the responding emergency services. “